001 /** 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, software 013 * distributed under the License is distributed on an "AS IS" BASIS, 014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018 019 package org.apache.hadoop.mapred; 020 021 import org.apache.hadoop.classification.InterfaceAudience; 022 import org.apache.hadoop.classification.InterfaceStability; 023 import org.apache.hadoop.conf.Configuration; 024 import org.apache.hadoop.fs.Path; 025 026 /** 027 * Utility class for skip bad records functionality. It contains various 028 * settings related to skipping of bad records. 029 * 030 * <p>Hadoop provides an optional mode of execution in which the bad records 031 * are detected and skipped in further attempts. 032 * 033 * <p>This feature can be used when map/reduce tasks crashes deterministically on 034 * certain input. This happens due to bugs in the map/reduce function. The usual 035 * course would be to fix these bugs. But sometimes this is not possible; 036 * perhaps the bug is in third party libraries for which the source code is 037 * not available. Due to this, the task never reaches to completion even with 038 * multiple attempts and complete data for that task is lost.</p> 039 * 040 * <p>With this feature, only a small portion of data is lost surrounding 041 * the bad record, which may be acceptable for some user applications. 042 * see {@link SkipBadRecords#setMapperMaxSkipRecords(Configuration, long)}</p> 043 * 044 * <p>The skipping mode gets kicked off after certain no of failures 045 * see {@link SkipBadRecords#setAttemptsToStartSkipping(Configuration, int)}</p> 046 * 047 * <p>In the skipping mode, the map/reduce task maintains the record range which 048 * is getting processed at all times. Before giving the input to the 049 * map/reduce function, it sends this record range to the Task tracker. 050 * If task crashes, the Task tracker knows which one was the last reported 051 * range. On further attempts that range get skipped.</p> 052 */ 053 @InterfaceAudience.Public 054 @InterfaceStability.Stable 055 public class SkipBadRecords { 056 057 /** 058 * Special counters which are written by the application and are 059 * used by the framework for detecting bad records. For detecting bad records 060 * these counters must be incremented by the application. 061 */ 062 public static final String COUNTER_GROUP = "SkippingTaskCounters"; 063 064 /** 065 * Number of processed map records. 066 * @see SkipBadRecords#getAutoIncrMapperProcCount(Configuration) 067 */ 068 public static final String COUNTER_MAP_PROCESSED_RECORDS = 069 "MapProcessedRecords"; 070 071 /** 072 * Number of processed reduce groups. 073 * @see SkipBadRecords#getAutoIncrReducerProcCount(Configuration) 074 */ 075 public static final String COUNTER_REDUCE_PROCESSED_GROUPS = 076 "ReduceProcessedGroups"; 077 078 private static final String ATTEMPTS_TO_START_SKIPPING = 079 JobContext.SKIP_START_ATTEMPTS; 080 private static final String AUTO_INCR_MAP_PROC_COUNT = 081 JobContext.MAP_SKIP_INCR_PROC_COUNT; 082 private static final String AUTO_INCR_REDUCE_PROC_COUNT = 083 JobContext.REDUCE_SKIP_INCR_PROC_COUNT; 084 private static final String OUT_PATH = JobContext.SKIP_OUTDIR; 085 private static final String MAPPER_MAX_SKIP_RECORDS = 086 JobContext.MAP_SKIP_MAX_RECORDS; 087 private static final String REDUCER_MAX_SKIP_GROUPS = 088 JobContext.REDUCE_SKIP_MAXGROUPS; 089 090 /** 091 * Get the number of Task attempts AFTER which skip mode 092 * will be kicked off. When skip mode is kicked off, the 093 * tasks reports the range of records which it will process 094 * next to the TaskTracker. So that on failures, TT knows which 095 * ones are possibly the bad records. On further executions, 096 * those are skipped. 097 * Default value is 2. 098 * 099 * @param conf the configuration 100 * @return attemptsToStartSkipping no of task attempts 101 */ 102 public static int getAttemptsToStartSkipping(Configuration conf) { 103 return conf.getInt(ATTEMPTS_TO_START_SKIPPING, 2); 104 } 105 106 /** 107 * Set the number of Task attempts AFTER which skip mode 108 * will be kicked off. When skip mode is kicked off, the 109 * tasks reports the range of records which it will process 110 * next to the TaskTracker. So that on failures, TT knows which 111 * ones are possibly the bad records. On further executions, 112 * those are skipped. 113 * Default value is 2. 114 * 115 * @param conf the configuration 116 * @param attemptsToStartSkipping no of task attempts 117 */ 118 public static void setAttemptsToStartSkipping(Configuration conf, 119 int attemptsToStartSkipping) { 120 conf.setInt(ATTEMPTS_TO_START_SKIPPING, attemptsToStartSkipping); 121 } 122 123 /** 124 * Get the flag which if set to true, 125 * {@link SkipBadRecords#COUNTER_MAP_PROCESSED_RECORDS} is incremented 126 * by MapRunner after invoking the map function. This value must be set to 127 * false for applications which process the records asynchronously 128 * or buffer the input records. For example streaming. 129 * In such cases applications should increment this counter on their own. 130 * Default value is true. 131 * 132 * @param conf the configuration 133 * @return <code>true</code> if auto increment 134 * {@link SkipBadRecords#COUNTER_MAP_PROCESSED_RECORDS}. 135 * <code>false</code> otherwise. 136 */ 137 public static boolean getAutoIncrMapperProcCount(Configuration conf) { 138 return conf.getBoolean(AUTO_INCR_MAP_PROC_COUNT, true); 139 } 140 141 /** 142 * Set the flag which if set to true, 143 * {@link SkipBadRecords#COUNTER_MAP_PROCESSED_RECORDS} is incremented 144 * by MapRunner after invoking the map function. This value must be set to 145 * false for applications which process the records asynchronously 146 * or buffer the input records. For example streaming. 147 * In such cases applications should increment this counter on their own. 148 * Default value is true. 149 * 150 * @param conf the configuration 151 * @param autoIncr whether to auto increment 152 * {@link SkipBadRecords#COUNTER_MAP_PROCESSED_RECORDS}. 153 */ 154 public static void setAutoIncrMapperProcCount(Configuration conf, 155 boolean autoIncr) { 156 conf.setBoolean(AUTO_INCR_MAP_PROC_COUNT, autoIncr); 157 } 158 159 /** 160 * Get the flag which if set to true, 161 * {@link SkipBadRecords#COUNTER_REDUCE_PROCESSED_GROUPS} is incremented 162 * by framework after invoking the reduce function. This value must be set to 163 * false for applications which process the records asynchronously 164 * or buffer the input records. For example streaming. 165 * In such cases applications should increment this counter on their own. 166 * Default value is true. 167 * 168 * @param conf the configuration 169 * @return <code>true</code> if auto increment 170 * {@link SkipBadRecords#COUNTER_REDUCE_PROCESSED_GROUPS}. 171 * <code>false</code> otherwise. 172 */ 173 public static boolean getAutoIncrReducerProcCount(Configuration conf) { 174 return conf.getBoolean(AUTO_INCR_REDUCE_PROC_COUNT, true); 175 } 176 177 /** 178 * Set the flag which if set to true, 179 * {@link SkipBadRecords#COUNTER_REDUCE_PROCESSED_GROUPS} is incremented 180 * by framework after invoking the reduce function. This value must be set to 181 * false for applications which process the records asynchronously 182 * or buffer the input records. For example streaming. 183 * In such cases applications should increment this counter on their own. 184 * Default value is true. 185 * 186 * @param conf the configuration 187 * @param autoIncr whether to auto increment 188 * {@link SkipBadRecords#COUNTER_REDUCE_PROCESSED_GROUPS}. 189 */ 190 public static void setAutoIncrReducerProcCount(Configuration conf, 191 boolean autoIncr) { 192 conf.setBoolean(AUTO_INCR_REDUCE_PROC_COUNT, autoIncr); 193 } 194 195 /** 196 * Get the directory to which skipped records are written. By default it is 197 * the sub directory of the output _logs directory. 198 * User can stop writing skipped records by setting the value null. 199 * 200 * @param conf the configuration. 201 * @return path skip output directory. Null is returned if this is not set 202 * and output directory is also not set. 203 */ 204 public static Path getSkipOutputPath(Configuration conf) { 205 String name = conf.get(OUT_PATH); 206 if(name!=null) { 207 if("none".equals(name)) { 208 return null; 209 } 210 return new Path(name); 211 } 212 Path outPath = FileOutputFormat.getOutputPath(new JobConf(conf)); 213 return outPath==null ? null : new Path(outPath, 214 "_logs"+Path.SEPARATOR+"skip"); 215 } 216 217 /** 218 * Set the directory to which skipped records are written. By default it is 219 * the sub directory of the output _logs directory. 220 * User can stop writing skipped records by setting the value null. 221 * 222 * @param conf the configuration. 223 * @param path skip output directory path 224 */ 225 public static void setSkipOutputPath(JobConf conf, Path path) { 226 String pathStr = null; 227 if(path==null) { 228 pathStr = "none"; 229 } else { 230 pathStr = path.toString(); 231 } 232 conf.set(OUT_PATH, pathStr); 233 } 234 235 /** 236 * Get the number of acceptable skip records surrounding the bad record PER 237 * bad record in mapper. The number includes the bad record as well. 238 * To turn the feature of detection/skipping of bad records off, set the 239 * value to 0. 240 * The framework tries to narrow down the skipped range by retrying 241 * until this threshold is met OR all attempts get exhausted for this task. 242 * Set the value to Long.MAX_VALUE to indicate that framework need not try to 243 * narrow down. Whatever records(depends on application) get skipped are 244 * acceptable. 245 * Default value is 0. 246 * 247 * @param conf the configuration 248 * @return maxSkipRecs acceptable skip records. 249 */ 250 public static long getMapperMaxSkipRecords(Configuration conf) { 251 return conf.getLong(MAPPER_MAX_SKIP_RECORDS, 0); 252 } 253 254 /** 255 * Set the number of acceptable skip records surrounding the bad record PER 256 * bad record in mapper. The number includes the bad record as well. 257 * To turn the feature of detection/skipping of bad records off, set the 258 * value to 0. 259 * The framework tries to narrow down the skipped range by retrying 260 * until this threshold is met OR all attempts get exhausted for this task. 261 * Set the value to Long.MAX_VALUE to indicate that framework need not try to 262 * narrow down. Whatever records(depends on application) get skipped are 263 * acceptable. 264 * Default value is 0. 265 * 266 * @param conf the configuration 267 * @param maxSkipRecs acceptable skip records. 268 */ 269 public static void setMapperMaxSkipRecords(Configuration conf, 270 long maxSkipRecs) { 271 conf.setLong(MAPPER_MAX_SKIP_RECORDS, maxSkipRecs); 272 } 273 274 /** 275 * Get the number of acceptable skip groups surrounding the bad group PER 276 * bad group in reducer. The number includes the bad group as well. 277 * To turn the feature of detection/skipping of bad groups off, set the 278 * value to 0. 279 * The framework tries to narrow down the skipped range by retrying 280 * until this threshold is met OR all attempts get exhausted for this task. 281 * Set the value to Long.MAX_VALUE to indicate that framework need not try to 282 * narrow down. Whatever groups(depends on application) get skipped are 283 * acceptable. 284 * Default value is 0. 285 * 286 * @param conf the configuration 287 * @return maxSkipGrps acceptable skip groups. 288 */ 289 public static long getReducerMaxSkipGroups(Configuration conf) { 290 return conf.getLong(REDUCER_MAX_SKIP_GROUPS, 0); 291 } 292 293 /** 294 * Set the number of acceptable skip groups surrounding the bad group PER 295 * bad group in reducer. The number includes the bad group as well. 296 * To turn the feature of detection/skipping of bad groups off, set the 297 * value to 0. 298 * The framework tries to narrow down the skipped range by retrying 299 * until this threshold is met OR all attempts get exhausted for this task. 300 * Set the value to Long.MAX_VALUE to indicate that framework need not try to 301 * narrow down. Whatever groups(depends on application) get skipped are 302 * acceptable. 303 * Default value is 0. 304 * 305 * @param conf the configuration 306 * @param maxSkipGrps acceptable skip groups. 307 */ 308 public static void setReducerMaxSkipGroups(Configuration conf, 309 long maxSkipGrps) { 310 conf.setLong(REDUCER_MAX_SKIP_GROUPS, maxSkipGrps); 311 } 312 }